Sachiko Hayakawa

Human young children as well as adults demonstrate 'superior' rapid snake detection when typical striking posture is displayed by the snake.

Humans as well as some nonhuman primates have an evolved predisposition to associate snakes with fear by detecting their presence as fear-relevant stimuli more rapidly than fear-irrelevant ones. In the present experiment, a total of 74 of 3- to 4-year-old children and adults were asked to find a single target black-and-white photo of a snake among an array of eight black-and-white photos of flowers as distracters. As target stimuli, we prepared two groups of snake photos, one in which a typical striking posture was displayed by a snake and the other in which a resting snake was shown. When reaction time to find the snake photo was compared between these two types of the stimuli, its mean value was found to be significantly smaller for the photos of snakes displaying striking posture than for the photos of resting snakes in both the adults and children. These findings suggest the possibility that the human perceptual bias for snakes per se could be differentiated according to the difference of the degree to which their presence acts as a fear-relevant stimulus.

The influence of color on snake detection in visual search in human children

It is well known that adult humans detect snakes as targets more quickly than flowers as the targets and that how rapidly they detect a snake picture does not differ whether the images are in color or gray-scale, whereas they find a flower picture more rapidly when the images are in color than when the images are gray-scale. In the present study, a total of 111 children were presented with 3-by-3 matrices of images of snakes and flowers in either color or gray-scale displays. Unlike the adults reported on previously, the present participants responded to the target faster when it was in color than when it was gray-scale, whether the target was a snake or a flower, regardless of their age. When detecting snakes, human children appear to selectively attend to their color, which would contribute to the detection being more rapidly at the expense of its precision.

Urine as another potential source for template DNA in polymerase chain reaction (PCR)

This technical note examines the potential for preparing template DNA in polymerase chain reactions (PCR) from urine in Japanese macaques (Macaca fuscata). Microsatellite band patterns from urine samples showed close agreement with those of blood and fecal samples, and only a few hundred μl of urine yielded a template DNA for PCR. This research will increase the opportunity for scientists to examine the genetic backgrounds of their target animals by using non‐invasive sample collection in the wild. Am. J. Primatol. 48:299–304, 1999.

Female Defensibility in a Small Troops of Japanese Macaques vis-à-vis Nontroop Males and Copulation on the Periphery of the Troop

I provide data compiled over 4 yr on the mating behavior in small troops of wild Japanese macaques on Yakushima Island. The key parameters are the number of sexually receptive females, the number of nontroop males (NTMs), and copulation on the periphery of the troop. I analyzed the following aspects: 1) changes in the proportion of copulation with high-ranking males (HRMs) and NTMs, 2) variations in factors such as fluctuation in the number of sexually receptive females and troop males and their effects on the number of visiting NTMs, 3) the effect of attempted interruption of mounting series by other males, and 4) some aspects of copulation on the periphery of the troop. Throughout the study, 56% of the total number of females mated most frequently with the α-male in a single mating season. However, the relative mating success of HRMs varied over the years and between individuals. The number of visiting NTMs varied depending on the number of receptive females and troop males. Females tended to mate with the NTMs when they appeared around their troops. The direct effect of interruption of the mounting series by other males is equivocal. The females mated with the low-ranking males (LRMs) and NTMs on the periphery of the troop, which increased the possibility of mounting series ending with ejaculation. Females actively sought opportunities for copulation on the periphery of the troop by moving there or initiating close proximity with LRMs and NTMs there. On Yakushima Island, the mating success of HRMs was not always as high as that predicted by the priority of access model. The injury status of the HRM, the number of visiting NTMs, and female choice are all considered to influence a male’s mating success.

Mass mortality of Japanese macaques in a western coastal forest of Yakushima

The mass mortality of wild Japanese macaques (Macaca fuscata Blyth) was observed in a warm temperate forest of Yakushima, southern Japan. Demographic changes of eight troops between August 1998 and August 1999 were studied and 56% of macaques disappeared from the five intensively studied troops. Mortality varied among troops: two troops became extinct, while another troop did not decrease in size. The rate of mortality of the other troops was between 33 and 80%. The variation in mortality among the troops was either the outcome of local concentrations of mortality or of intertroop competition. The rate of mortality decreased with increasing distance from the two extinct troops and with increasing troop size; these two factors could not be separated statistically. The direct cause of death was diagnosed as pneumonia for four out of five fresh carcasses. The fleshy fruit production in autumn 1998 was the lowest in 14 years, and macaques had relied on leaves earlier than in usual years. It was exceptionally hot and dry in the summer of 1998. The exceptionally poor fruit production and hot summer of this year, with the resulting shortage of high-quality foods, was consistent with the scenario that mass mortality was due to the poor nutritional conditions. However, the possibility that epidemics caused the mass mortality cannot be ruled out. Our findings proved that primates in a seemingly stable habitat experience fluctuations in demographic parameters under natural conditions.

Male-female mating tactics and paternity of wild Japanese Macaques (Macaca fuscata yakui).

For Japanese macaques, visits by nontroop males (NTMs) often diminish the immediate copulation success of high‐ranking males, although few studies have conducted a genetic analysis to show their contribution to the gene pool. I used noninvasively collected samples of semen, blood, urine and feces for the analysis of paternity in nine offspring born in two troops living on the island of Yakushima, Japan. I found that five of the nine offspring were sired by NTMs. It is argued that social change, small troop size and the timing of conception are all factors contributing to the NTMs reproductive success. Am. J. Primatol. 70:986–989, 2008.

Skewed Matrilineal Genetic Composition in a Small Wild Chimpanzee Community

Maternal kinship is important in primate societies because it affects individual behaviour as well as the sustainability of populations. All members of the Bossou chimpanzee community are descended from 8 individuals (herein referred to as original adults) who were already adults or subadults when field observations were initiated in 1976 and whose genetic relationships were unknown. Sequencing of the control region on the maternally inherited mtDNA revealed that 4 (1 male and 3 females) of the 8 original adults shared an identical haplotype. We investigated the effects of the skewed distribution of mtDNA haplotypes on the following two outcomes. First, we demonstrated that the probability of mtDNA haplotype extinction would be increased under such a skewed composition in a small community. Second, the ratio of potential mating candidates to competitors is likely to decrease if chimpanzees become aware of maternal kinship and avoid incest. We estimated that the magnitude of the decrease in the ratio is 10 times greater in males than in females. Here we demonstrate a scenario in which this matrilineal skewness in a small community accelerates extinction of mtDNA haplotype, which will make it more difficult to find a suitable mate within the community.

Conserved evolutionary history for quick detection of threatening faces.

Humans quickly recognize threats such as snakes and threatening faces, suggesting that human ancestors evolved specialized visual systems to detect biologically relevant threat stimuli. Although non-human primates also detect snakes quickly, it is unclear whether primates share the efficient visual systems to process the threatening faces of their conspecifics. Primates may not necessarily process conspecific threats by facial expressions, because threats from conspecifics in natural situations are often accompanied by other cues such as threatening actions (or attacks) and vocal calls. Here, we show a similar threat superiority effect in both humans and macaque Japanese monkeys. In visual search tasks, monkeys and humans both responded to pictures of a threatening face of an unfamiliar adult male monkey among neutral faces faster than to pictures of a neutral face among threatening faces. However, the monkeys’ response times to detect deviant pictures of a non-face stimulus were not slower when it was shown among threat faces than when it was shown among neutral faces. These results provide the first evidence that monkeys have an attentional bias toward the threatening faces of conspecifics and suggest that threatening faces are evolutionarily relevant fear stimuli. The subcortical visual systems in primates likely process not only snakes, but also more general biological threat-relevant stimuli, including threatening conspecific faces.

The convergent evolution of blue iris pigmentation in primates took distinct molecular paths

How many distinct molecular paths lead to the same phenotype? One approach to this question has been to examine the genetic basis of convergent traits, which likely evolved repeatedly under a shared selective pressure. We investigated the convergent phenotype of blue iris pigmentation, which has arisen independently in four primate lineages: humans, blue-eyed black lemurs, Japanese macaques, and spider monkeys. Characterizing the phenotype across these species, we found that the variation within the blue-eyed subsets of each species occupies strongly overlapping regions of CIE L*a*b* color space. Yet whereas Japanese macaques and humans display continuous variation, the phenotypes of blue-eyed black lemurs and their sister species (whose irises are brown) occupy more clustered subspaces. Variation in an enhancer of OCA2 is primarily responsible for the phenotypic difference between humans with blue and brown irises. In the orthologous region, we found no variant that distinguishes the two lemur species or associates with quantitative phenotypic variation in Japanese macaques. Given the high similarity between the blue iris phenotypes in these species and that in humans, this finding implies that evolution has used different molecular paths to reach the same end. Am J Phys Anthropol 151:398–407, 2013.© 2013 Wiley Periodicals, Inc.

Troop Takeover and Reproductive Success of Wild Male Japanese Macaques on Yakushima Island (Macaca fuscata yakui)

Troop takeover is common in one-male primate groups, but there are few reports in multimale groups. Japanese macaques (Macaca fuscata) form multimale groups and males commonly join troops at the bottom rank. On Yakushima island, however, where group size is relatively small, entrance into groups at the alpha position is also observed. This paper reports on the general features of troop takeover, on the predictors of takeover events, and on the reproductive success of takeover males. Troop takeovers occurred only in the mating season; nontroop males (NTMs) did not cooperate with each other; former alpha males were rarely expelled from the troop; new alpha males did not commit infanticide; new alpha male tenure in the group was usually less than two years. Logistic regression analysis showed that the number of NTMs associating with a troop predicted the occurrence of troop takeover. Paternity discrimination revealed that 33.3% (3/9) of takeover males succeeded in siring offspring. Contrary to this low success rate, binary logistic regression analysis revealed that the takeover males can expect higher reproductive success compared to troop males. Entering a troop and out-competing the alpha male is one of many available strategies to attain reproductive success in male Japanese macaques.